Crowd-Pleasing Potato Pizza

3 potatoes, peeled and cubed
10-oz. tube refrigerated pizza crust

1/4 c. milk
1/2 t. salt
1-lb. pkg. bacon, diced
1 onion, chopped
1/2 c. red pepper, chopped
1-1/2 c. shredded Cheddar cheese
1-1/2 c. shredded mozzarella cheese
Optional: sour cream

Place potatoes in a large saucepan; barely cover with water. Boil until tender, about 20 to 25 minutes; drain and set aside. Flatten pizza dough on an ungreased 14" pizza pan; pinch edges to form a rim. Prick dough with a fork; bake at 350 degrees until golden, about 15 minutes. Cool on a wire rack. Transfer potatoes to a mixing bowl; add milk and salt. Mash until smooth; spread over crust. Slightly brown bacon; add onion and pepper and cook until tender. Drain and spread over potatoes. Sprinkle with cheeses; bake at 375 degrees for 20 minutes. Cut into wedges to serve; spread with sour cream, if desired. Makes 8 servings.